Semiconductor rectifier devices for rectifying and outputting input current include a PiN diode having a pn junction and a Schottky barrier diode (SBD) having a carrier potential barrier caused by difference between work functions of metal and a semiconductor layer. In addition, in the Schottky barrier diode, there is also a JBS (Junction Barrier Schottky barrier diode) in which an impurity region (for example, p-type) having a conductivity type different from the semiconductor layer is arranged on the semiconductor layer surface for the purpose of alleviating an electric field applied onto the interface between the metal and the semiconductor layer (for example, n-type). Further, there is also an MPS (Merged PiN-diode Schottky-diode) in which the contact between the metal and the impurity region (for example, p-type) of the JBS is made to be ohmic connection or almost ohmic connection, and when a voltage more than a built-in potential (Vbi) between the impurity region and the semiconductor layer is applied, minority carriers are injected, so that this provides a function of reducing the resistance by conductivity modulation.
On the other hand, a wide band gap semiconductor such as a silicon carbide (which will be hereinafter referred to as SiC) is expected as a next-generation power semiconductor device material. The wide band gap semiconductor has a wider band gap than Si, and has a higher break-down electric field intensity and a higher thermal conductivity rate than Si. When this property is utilized, a low-loss power semiconductor device capable of operating at a high temperature can be realized.
In the MPS, a voltage causing the conductivity modulation is reduced, whereby the forward property has a lower resistance, and when a forward surge current flows in, a large current can be discharged with a low forward voltage. When a larger current than that of a normal state flows, the current causes junction break-down of an electrode and the like and crystal break-down caused by the heat generated according to the formula, current×voltage=energy. However, when a large current can be passed with a low forward voltage, exothermic energy can be suppressed, and this reduces break-down rate of the device.